A plasma processing device such as a plasma etching device, which is capable of performing various types of plasma processing, is utilized during a semiconductor device manufacturing process in the related art. Such a device processes a workpiece placed within a process chamber by generating plasma inside the process chamber with the pressure of its atmosphere sustained at a level lowered to a preset level. In addition, the pressure inside the process chamber is adjusted by controlling a pressure (evacuation quantity) control valve based upon pressure data provided by a pressure sensor.
As ultra high integration and super multi-layer structures are becoming increasingly common in semiconductor devices in recent years, a plurality of films constituted of different materials sometimes must be etched through continuous processing. During such processing, the pressure inside the process chamber may need to be raised/lowered in correspondence to the material constituting a given film. Some film materials require the processing to be executed at a low pressure of approximately several Pa. In addition, a pressure detection range over which detection is enabled is set for the pressure sensor and the pressure detection range of a pressure sensor capable of detecting a low pressure with a high degree of accuracy tends to be smaller under normal circumstances. For this reason, pressure data to be used in pressure control are sometimes obtained by switching among a plurality of pressure sensors as appropriate so as to detect the processing pressure levels at which the individual films are processed and to monitor the overall change in the pressure occurring inside the process chamber.
However, the processing device in the related art described above switches to a given pressure sensor among the individual pressure sensors based upon switching information that is set in advance. Namely, the pressure controller does not automatically switch among the various pressure sensors based upon the pressure data provided by the individual pressure sensors. As a result, it is difficult to obtain pressure data that reflect a drastic pressure change since the selection of the appropriate pressure sensor cannot be made promptly when the pressure inside the process chamber changes greatly. Thus, a problem arises in that the resulting delay in the control on the pressure inside the process chamber tends to cause inconsistency in the processing.
In addition, an increasing need to achieve super-miniaturization of semiconductor devices in recent years necessitates super-miniaturization processing to be implemented on a workpiece during an etching process, as well. When the workpiece undergoes the super-miniaturization processing, the pressure inside the process chamber must be rigorously adjusted to sustain the level of the pressure inside the process chamber at a predetermined level. Accordingly, accurate pressure control must be achieved through a finer analysis of pressure data provided by a pressure sensor. However, if the detected pressure is finely analyzed over a pressure range that does not affect the processing, too, the length of time required for the arithmetic processing increases. This may lead to a problem in that the response of the pressure control valve becomes poor.
An object of the present invention, which has been completed by addressing the problems of the related art discussed above, is to provide a new and improved pressure control method and a new and improved plasma processing device that provide a solution to problems identified above and other problems as well.